Tornado threat for the Plains...

[senorpepr]

URGENT - IMMEDIATE BROADCAST REQUESTED
TORNADO WATCH NUMBER 311
NWS STORM PREDICTION CENTER NORMAN OK
500 PM CDT SAT MAY 21 2005

THE NWS STORM PREDICTION CENTER HAS ISSUED A
TORNADO WATCH FOR PORTIONS OF

WESTERN IOWA
NORTHEASTERN KANSAS
FAR NORTHWESTERN MISSOURI
EASTERN NEBRASKA
EXTREME SOUTHEASTERN SOUTH DAKOTA

EFFECTIVE THIS SATURDAY AFTERNOON AND EVENING FROM 500 PM UNTIL
1000 PM CDT.

TORNADOES...HAIL TO 3 INCHES IN DIAMETER...THUNDERSTORM WIND GUSTS
TO 70 MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.

THE TORNADO WATCH AREA IS APPROXIMATELY ALONG AND 65 STATUTE MILES
EAST AND WEST OF A LINE FROM 55 MILES NORTH NORTHEAST OF SIOUX
CITY IOWA TO 5 MILES SOUTHEAST OF MANHATTAN KANSAS. FOR A
COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH OUTLINE
UPDATE (WOUS64 KWNS WOU1).

REMEMBER...A TORNADO WATCH MEANS CONDITIONS ARE FAVORABLE FOR
TORNADOES AND SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH AREA.
PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR THREATENING
WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS AND POSSIBLE
WARNINGS.

OTHER WATCH INFORMATION...CONTINUE...WW 310...

DISCUSSION...THUNDERSTORMS EXPECTED TO DEVELOP AND QUICKLY BECOME
SEVERE ALONG STRONG SURFACE FRONT EXTENDING FROM NEAR YKN TO NEAR
CNK AT 21Z. FRONT WILL SHIFT EWD AND AID IN BREAKING STRONG CAP
ACROSS WW THROUGH THE EVENING. VERY STEEP LAPSE RATES AND STRONG
SHEAR WILL SUPPORT SUPERCELLS WITH ATTENDANT THREAT OF VERY LARGE
HAIL AND DAMAGING WINDS. TORNADOES MAY OCCUR WITH PERSISTENT
SUPERCELLS...ESPECIALLY INTO ERN NEB AND WRN IA WHERE LCLS REMAIN
LOWER AND STORMS MAY MOVE NEAR OUTFLOW BOUNDARY FROM EARLIER STORMS.
ACTIVITY MAY CONSOLIDATE INTO AN MCS/BOW ECHO WITH INCREASED THREAT
OF DAMAGING WINDS TOWARDS THE MID EVENING.

AVIATION...TORNADOES AND A FEW SEVERE THUNDERSTORMS WITH HAIL
SURFACE AND ALOFT TO 3 INCHES. EXTREME TURBULENCE AND SURFACE WIND
GUSTS TO 60 KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 500.
MEAN STORM MOTION VECTOR 25020.


...EVANS




MESOSCALE DISCUSSION 0954
NWS STORM PREDICTION CENTER NORMAN OK
0350 PM CDT SAT MAY 21 2005

CAP STRENGTH BEING MONITORED ACROSS ERN NEB WHERE AIR MASS CONTINUED
TO DESTABILIZE THIS AFTERNOON WITH MLCAPE VALUES UP TO 2000 J/KG
WITHIN NARROW INSTABILITY AXIS. ONCE STORMS DEVELOP...SUPERCELLS
WILL BE LIKELY GIVEN 40-50 KT DEEP LAYER SHEAR VECTORS ORIENTED
NEARLY PERPENDICULAR TO THE SURFACE BOUNDARIES.

..PETERS.. 05/21/2005

[Brett Adair]

Yes, some small convective showers and trying to punch through the cap which has been decaying pretty rapidly for the last 3 hrs. Temps at OAX went from about 14C at 700mb to 9C in the last three hours or so. Looking at a mesoanalysis loop things may fire along a SFC vort axis initially in SE NE/NE KS. It is going to be rough with that high CINH though.

[Guest]

It is not looking too good. That cap is definitely hanging in there. The only things I see to my west as of 7pm are cirrus with a small cumulus TRYING to develop. I forsee the tornado watch for my area being canceled by 8pm if nothing of significance develops. I was thinking SPC may have upgraded to Moderate risk, thankfully, for them, they did not!

[AirmaN]

Woohoo!! First time I haven't been at work during a tornado watch this year!!!!

[jkt21787]

Cap remains very strong, against what all models and forecast soundings had indicated, CINH remains very high, and some sounding info indicates LSI of over 2 and convective temps of 95+. Needless to say thats tough to break, and with the cooling process beginning shortly the situation will get tougher.

Nevertheless, the atmosphere is extremely favorable. Very unstable and highly sheared. SCP has been over 30 (values I have never recalled seeing), and EHI up to 10 in the lowest 1km. CAPE values well over 3000 in some areas as well, with lapse rates remaining steep. It is an awesome setup, and if the cap was broken, we would be dealing with some supercell tornadoes right now, no doubt.

However, cap has not broken, and SPC says they are getting doubtful as well. They will maintain the watch for a while longer. The cap will eventually break, but it will likely be well after dark as instability decreases. Definitely looks bust for the chasers. We still could get some well organized storms though that possible evolve into an MCS and move ESE towards MO overnight.

[senorpepr]

MESOSCALE DISCUSSION 0956
NWS STORM PREDICTION CENTER NORMAN OK
0726 PM CDT SAT MAY 21 2005

VERY UNSTABLE AND HIGHLY SHEARED ENVIRONMENT REMAINS STRONGLY CAPPED
TO SFC-BASED CONVECTION OVER THE BULK OF TORNADO WATCH 311 THIS
EVENING. EARLIER ATTEMPTS AT STORM INITIATION NEAR FRONT BOUNDARY
INTERSECTION OVER EXTREME SERN NEB HAVE FAILED AS CELLS DRIFTED SEWD
OFF THE BOUNDARY AND DECAYED OVER NERN KS. ANOTHER UPDRAFT APPEARED
TO COINCIDE WITH COLD FRONT/REMNANT OUTFLOW INTERSECTION ACROSS SERN
SD. THIS CELL HAS ALSO WEAKENED/DIMINISHED. HOWEVER... ADDITIONAL
ACTIVITY APPEARS TO BE OCCURRING NEAR THE FRONT IN EXTREME SERN SD
WHERE CAP MAY BE WEAKEST.

CLEARLY...CAP IS SUPPRESSING DEEP CONVECTION DESPITE ALMOST ALL
SHORT-TERM GUIDANCE SUGGESTING OTHERWISE. OMA/TOP RAOBS INDICATED
NEARLY 200 J/KG MLCIN AND WITH DIURNAL BOUNDARY LAYER COOLING NOW
SETTING IN...PROSPECTS FOR WIDESPREAD DEVELOPMENT APPEAR TO BE
DIMINISHING. NONETHELESS...ENVIRONMENT ACROSS THE SRN PORTIONS OF
THE WATCH REMAINS VERY FAVORABLE FOR SUPERCELLS. EVEN ONE STORM IN
THIS ENVIRONMENT COULD QUICKLY BECOME SEVERE. THUS...WATCH WILL BE
MAINTAINED ACROSS THE REGION FOR AT LEAST ANOTHER COUPLE MORE HOURS.

..CARBIN.. 05/22/2005

[senorpepr]

Cap remains very strong, against what all models and forecast soundings had indicated, CINH remains very high, and some sounding info indicates LSI of over 2 and convective temps of 95+. Needless to say thats tough to break, and with the cooling process beginning shortly the situation will get tougher.

Nevertheless, the atmosphere is extremely favorable. Very unstable and highly sheared. SCP has been over 30 (values I have never recalled seeing), and EHI up to 10 in the lowest 1km. CAPE values well over 3000 in some areas as well, with lapse rates remaining steep. It is an awesome setup, and if the cap was broken, we would be dealing with some supercell tornadoes right now, no doubt.

However, cap has not broken, and SPC says they are getting doubtful as well. They will maintain the watch for a while longer. The cap will eventually break, but it will likely be well after dark as instability decreases. Definitely looks bust for the chasers. We still could get some well organized storms though that possible evolve into an MCS and move ESE towards MO overnight.

I completely agree. So much is there, but one key thing is holding it back -- the capping.

[Guest]

The capping, or on the flip side, that dang cirrus. That has held down our heating to break the cap. We were forecast to reach 90 or so today, but only hit 84 here in Omaha.

If we had hit our forecast high, cirrus-free, I would not be typing this right now.

[jkt21787]

Cap remains very strong, against what all models and forecast soundings had indicated, CINH remains very high, and some sounding info indicates LSI of over 2 and convective temps of 95+. Needless to say thats tough to break, and with the cooling process beginning shortly the situation will get tougher.

Nevertheless, the atmosphere is extremely favorable. Very unstable and highly sheared. SCP has been over 30 (values I have never recalled seeing), and EHI up to 10 in the lowest 1km. CAPE values well over 3000 in some areas as well, with lapse rates remaining steep. It is an awesome setup, and if the cap was broken, we would be dealing with some supercell tornadoes right now, no doubt.

However, cap has not broken, and SPC says they are getting doubtful as well. They will maintain the watch for a while longer. The cap will eventually break, but it will likely be well after dark as instability decreases. Definitely looks bust for the chasers. We still could get some well organized storms though that possible evolve into an MCS and move ESE towards MO overnight.

I completely agree. So much is there, but one key thing is holding it back -- the capping.

Yeah, I was a little excited today, because I just purchased Live Level II radar data today and was obviously looking for something to track. I hadn't paid attention much to this system, but noticed the SPC risk area. The models looked pretty good so was hoping for some big supercells to track. Watching the SPC Mesoanalysis today was fun as the parameters went way more favorable than indicated for tornadic development, then of course the T-watch going up. The only thing negative as far as parameters was the LCL height which was high and meant perhaps more high-based storms.

Of course none of that matters when the cap is strong. I saw it was going to be a problem, but nothing near this bad given all of the models breaking out precip around 00z time frame.

Maybe I'll have something to track, and you something to experience for yourself. Good luck and maybe this cap can break soon.

[jkt21787]

The capping, or on the flip side, that dang cirrus. That has held down our heating to break the cap. We were forecast to reach 90 or so today, but only hit 84 here in Omaha.

If we had hit our forecast high, cirrus-free, I would not be typing this right now.

Yeah, I noticed some of the cirrus on the vis earlier and it crossed my mind about sfc heating, but it didn't look too thick. It obviously did hurt though, but some of the soundings indicated convective temps approaching 100 in a few locations!

[Guest]

About half of the tornado watch (west of Fremont to Wahoo, to Lincoln) have just been cleared from the watch box. I don't think it is going to last much longer for the remaining counties either.

[Guest]

Tornado Watch gone for the rest of the affected area. Just way too much cap and too little heating.

[jkt21787]

Tornado Watch gone for the rest of the affected area. Just way too much cap and too little heating.

Sorry guys. That cap just wouldn't budge at all.

[Guest]

What just gets me is that SPC now has an MCD up for westernIowa and north Missouri for a possible TSTM watch. I thought they were MORe stable then here in Omaha and westward with teh reminence of last nights storms stabilizing.

Oh, well, we have alot of storm season to go!

[AirmaN]

boooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo

[Guest]

Next storm chances forecast for Tuesday through Thursday. Actually, today (Saturday) was supposed to be a dry day anyway up until Wednesday when storm chances were moved up from Sunday to Saturday.

[Brett Adair]

Yesterday was just no hope for the area. Especially with convective temperatures per 21z RUC2 RUC FCST SNDG's convective temps of over 103°.